This is a prospective study of the effects of lead exposure on the physical and mental health of children. It is composed of both human and animal studies. The study of children is being conducted in the natural environmental setting where elevated lead exposure is common, in order to establish whether and under what environmental circumstances lead causes adverse health effects. Prospective mothers are being recruited into the study during the first or second trimester of pregnancy. Their offspring will be followed for five years. Since many factors are known to influence the behavioral and intellectual development of a child, a multivariate design is being used rather than a design which employs a control versus experimental group comparison. Data being collected on each child include: prenatal and delivery records; physical growth, behavioral and intellectual profiles beginning at 3 days of age and repeated at 9 month intervals; blood lead; FEP; and iron status at 3 month intervals; evaluation of the home environment with respect to quality of child care and sources of lead exposure. The animal studies use rats exposed perinatally to low levels of lead. Other measures include neurotransmitter metabolism and behavioral evaluation. The animal studies are exploring critical periods, persistence and reversibility of toxicity and the utility of hematopoietic indices for indentifying individuals at risk for subsequent behavioral impairment. Both human and animal studies are examining the role of age, duration and levels of lead exposure as determinants of effect as well as exploring leads interaction with numerous environmental variables as a determinant of toxicity.